Answer:-
If an element has 3 or more valence electrons then the element belongs to p block of the periodic table. For p block elements the group number is found out by adding the number of electrons in valence shell + 10.
The reason for this is because in the middle of the periodic table there are the d block elements ranging from group 3 to group 12 a total of 10 groups in between elements having 2 valence electrons and 3 valence electrons
